Traffic jams are not only bad for your mood - they may actually kill, research suggests.
A modern health menace?
A German study has found people caught in traffic are three times more likely to have a heart attack within the hour than those who are not stuck in a jam.
Scientists, who studied hundreds of heart attacks, concluded nearly one in 12 was linked to traffic. Women and the over-60s were particularly at risk.
The research is published in the New England Journal of Medicine.
The researchers say more work is required to determine whether the heart attacks are due to traffic-related stress or exposure to high levels of pollution.
This study certainly strengthens the arguments in favour of stronger measures to reduce pollution in our cities.
The study was based on interviews with 691 volunteers who survived a heart attack from 1999 to 2001.
The patients were asked to outline their activities during the four days before their attacks.
Being stuck in a traffic jam seemed to increase risk no matter what form of transport the patient was using.
Heart attacks were 2.6 times more common for people stuck in cars, 3.1 times higher for people taking public transportation, and 3.9 times greater for cyclists.
However, because people on public transport seemed to be at risk, the researchers believe that stress is unlikely to be the only factor.
Pollution probably key
Writing in the journal, the researchers, from the National Research Center for Environment and Health in Neuherberg, said: "Given our current knowledge, it is impossible to determine the relative contribution of risk factors such as stress and traffic-related air pollution.
"Nevertheless, patients who are at risk for acute coronary events are likely to profit from recent efforts to improve the air quality in urban areas with the use of cleaner vehicles and improved city planning."
Professor Jeremy Pearson, Associate Medical Director at the British Heart Foundation, said the study provided new insights into the possible triggers of heart attacks.
"Previous research has shown common suspects such as sudden strenuous exercise can be a trigger, as can air pollution.
"But while chronic stress is known to increase long-term risk of heart disease, the evidence that acute stress can trigger a heart attack is not strong.
"Since these patients had more than double the risk if they were in traffic shortly before their heart attack - regardless of whether they were in cars, public transport or on a bicycle - increased air pollution was the most likely trigger.
"Although it is difficult to rule out other factors such as stress, this study certainly strengthens the arguments in favour of stronger measures to reduce pollution in our cities."